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Since the first phase of wear is fairly linear as a function of the number of cycles and failure will occur soon after phase one wear, the base failure rate of the actuator can be approximated as follows: 106 Kc,B = T7- (9-14) Where: AAC,B = Base failure rate of actuator, failures/million cycles N0 = Number of cycles in constant wear phase (See Equation (9-6)) As noted in Equation (9-2), the ratio of Yield strength to compressive strength is raised to the 9th power creating a wide range of resulting failure rates in Equation (9-14) for small differences in material properties. Reliability testing may be required on a sample of actuators to duplicate the curves as shown in Figure 9.2. 9.3.2 Contaminant Multiplying Factor As established in Equation (9-1), the failure rate of the actuator can be determined as follows: ^AC = ^AC,B * CCP * CT Where: = Failure rate of actuator, failures/million cycles A,AQB = Base failure rate of actuator, failures/million cycles Cap = Contaminant multiplying factor CT = Temperature multiplying factor (See Section 9.3.3) During the time that the actuator is at rest, particles can work their way between the piston and cylinder. Then, when the actuator is put into motion, increased forces are needed to move the piston. This stiction phenomenon causes a loss of actuator response and in some severe cases, a completely jammed component. Three types of wear need to be considered in determining the effects of contaminants on actuator reliability: (1) Erosion - Particles carried in a fluid stream impact against the piston and cylinder surfaces. If the kinetic energy released upon actuator response is large Actuators 9-11 Revision C

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